By weathering of feldspars, which represent about 60% of all minerals, there results kaolinite, the main raw material of the ceramic industry. However, kaolinite also finds use as a filler material in the production of paper and cardboard, as well as in the synthetic resin, rubber and dyestuffs industries. The need for kaolinite for these fields of use is continuously increasing.
Since kaolinite does not occur in nature in pure form but rather in an admixture with feldspar and quartz, a purification or enrichment is necessary since high demands of quality are placed on the product. The working up technique is of increasing importance since in the future the ratio of kaolinite to feldspar and quartz will become worse to the disadvantage of kaolinite. Furthermore, besides substantially pure kaolinite, the working up process is also to provide feldspar in high concentration.
In the case of the flotation of kaolinite, there are used, inter alia, quarternary ammonium compounds as cationic-active collectors. These have a strongly toxic effect on living organisms, are not broken down biologically and, in addition, require a pH value higher than 3 and thus considerable amounts of acid.
The recovery of feldspar from the minerals used for obtaining kaolinite has, in the meantime, achieved worldwide importance. Hitherto, the flotation of these minerals has only been satisfactory with a combination of flotation agents containing hydrofluoric acid.
Besides the disadvantage of the use of cationic collectors, which is not without problems with regard to their toxicity, there is the additional problem of having to work with the toxic and corrosive hydrofluoric acid.
Thus, there is a need to develop a process which avoids the disadvantages of the previously known flotation processes for the separation of minerals or which makes possible a separation of types of gangue from ores and coal and permits the achievement of high yields of pure products.